Basics

Why another scrolling-text sign?

You’ve seen the LED dot-matrix signs in shops, bus-stops, etc which just scroll a long piece of text across a small window so that you only see 8 or so characters at once, but it’s nice and big.

If you do a search on Android market for such applications, there are plenty of results. But why, you might ask, does a digital sign need permissions to Know your location, Get details of your SIM card, Send anything it knows across the internet, etc?

It didn’t seem right somehow – an app should do just what it needs to do and not trick you into installing something dodgy. So I chose this as my first android app.

Fonts

Fonts for LED signs typically come as blocks binary information – each character is (e.g.) 7 x 5 pixels, each of which is on or off. The fonts come in a variety of forms, but often are just written as C/C++/Java static arrays. e.g. here’s one for 5-pixel high displays:

So you have a message, each character becomes a block of LEDs, you work-out which ones are visible on screen, and just draw a load of little rectangles depending on whether the font says on or off for each location. Simples.

One limitation is that most fonts typically come with just 128 or 256 glyphs, and use ASCII (or one of the ISO-8859 character-sets) to choose characters.

So don't use this app if you need to display Japanese characters or runes. But let me know if you find a nice bitmap font with some better unicode support?